1. Field of the Invention
The present invention relates to a visual acuity test mark displaying device (hereinafter referred to as "test mark displaying device") provided with a visual acuity test mark selecting means for selecting a desired visual acuity test mark (hereinafter referred to as "test mark") among a plurality of test marks.
2. Description of the Related Art
Recently, computer technology has been incorporated into vision testers, and vision testers provided with a microcomputer are prevalent in recent years. Computer-aided control techniques are applied to the control of test marks of vision test chart projectors and vision testers, such as backlighted vision test charts of a polar chart type and a panel type. These vision testers are provided with a remote controller for changing the test marks, operated by the tester in changing the test marks. A known vision tester cooperates with another apparatus, such as an refractor, i.e., what is called a motor-driven phoroptor, for efficient vision testing.
Incidentally, although Landolt rings are most prevalent test marks of the vision test chart, characters and marks other than Landolt rings are used in addition to Landolt rings. The combination and arrangement of these test characters and test marks are specified in national standards or determined by national or local convention. The vision tester is required to be capable of ophthalmic tests including an astigmatic vision test, a cross-cylinder test muscle barance test and a stereoscopic vision test etc., and these tests employ different test mark sets, respectively.
Accordingly, the vision tester manufacturers need to manufacture vision testers provided respectively with different types of vision test charts, and the test mark control program must be modified so as to meet the control of the vision test chart employed in the vision testers.
A procedure of modifying the visual test mark control program will be described in connection with a control circuit included in a conventional vision tester.
FIG. 1 shows the appearance of a remote controller for controlling a vision test chart projector. The arrangement of switches on the remote controller and test marks are dependent on user's option. FIG. 2 shows the circuit of the remote controller. When the chart selector switch 61 is depressed, a predetermined code digital signal is occurred by microcomputer 62, the signal is converted into a code optical pulse signal by a light emitting element 68 through code modulation circuit 64 and output buffer 66, and is transferred to the vision test chart projector. Generally, the switching circuit of the remote controller is a switching matrix because the remote controller deals with a plurality of test marks.
The following modifications are made in manufacturing a vision test chart projector to project a specified vision test chart.
1. A glass chart disk carrying various vision test charts formed thereon by photographic printing processes is fabricated.
2. Indications on the operating panel of the remote controller are changed.
3. The chart disk is driven by a motor and a table tabulating code signals representing individual test marks, and the corresponding number of pulses representing steps of operation of the motor is rewritten to make the operation of the selector keys provided on the operating panel of the remote controller coincide with that of the chart disk and, if necessary, a mask disk and the program is modified.
A vision tester which cooperates with a refractor, such as disclosed in Japanese Patent Application Laid-Open No. Sho 63(1988)-147429, controls both the vision tester and the refractor by means of the test mark selector key of the remote controller. A wireless remote controller employs a special IC chip capable of operating at a low power consumption so that the wireless remote controller can be driven by a battery. Therefore, the code signals determined by the switching matrix circuit of this vision tester, in most cases, do not coincide with those determined by the switching matrix circuit of the refractor. Accordingly, the code signals corresponding to the test mark selector switch of the controller of the refractor are converted into those provided by the wireless remote controller for controlling the vision tester. In this refractor, the following modifications are made, in addition to the modification of the program for controlling the refractor, to deal with the change of the test mark set.
1. Indications on the operating panel are changed.
2. The code signals provided by operating the operating panel are changed for the code signals for controlling the vision tester, and the program is modified.
3. A table tabulating the objects of operation of an electronic dial provided on the operating panel, and data for selecting the right and left auxiliary lenses is rewritten and the program is modified.
Problems requiring the inefficient manufacture of many types of vision testers cannot be solved unless an international standard test mark set is established. The modification of the program according to the change of the test mark set requires very complicated work. A vision tester that cooperates with another refractor, in particular, requires the modification of an extensive portion of the program including a portion specific to the control of the vision tester, which is a primary cause of increase in the manufacturing cost of the apparatus.